| 2 CYCLE ENGINES and their reliability |
| I really hate to hear people say that "2 cycle engines are not reliable" or vastly inferior to 4 cycle engines. Like most devices there are good and bad engines, but there is no correlation to the number of strokes in a cycle.
High performance 2 stroke engines can have cooling problems and cylinder - piston distortion due to the heat exposed to the piston that does "double duty". They also can really gobble fuel at an amazing rate depending on how highly tuned they are, and how many cylinders they have. In general most 2 stokes run at very low compression ratios, usually less than 7:1 and can use regular unleaded fuel. |
My own 582 Rotax engine showed very little wear at 1200 hours. ( above ) Important thing to watch for is stuck rings. The piston gets rid of it's heat mostly through the piston rings. A
stuck ring allows blow-by, and this takes the oil off of the cylinder wall. A seizure is then likely. Max deviation near the ports is .0015 inch. Above you can see some visible sreaks from
carbon below the exhaust port. You can still see plenty of the cross-hatch. This engine has original piston, cylinders, and rings.
You cannot check for stuck rings by looking in the exhaust port. They usually get stuck near the anti-rotation pin on the intake side of the piston.
When removing the rings to de carbon the grooves, be sure to keep the same ring on the same piston and the same face up. These parts are matched to the cylinder. They will last
for years if you do this properly.
New rings require honing, and if the engine has many hours, boring and honing to put the cylinder round. This gets more expensive.
If regular de-carboning is not done, rings can get so stuck, that a new piston and a bore job would be required, and this will be costly.
I am often asked what type oil I use: Pennzoil AIR COOLED, and de carbon at no more than 350 hours. ( I favor mineral oil and am not stuck on Pennzoil, but it works very well.)
It costs me very little to keep my engine running, but I do my own work. The Rotax does require some special tools to work on it, but they are not expensive. I make my own tools as
shown above. One tool helps pop those wrist pin circlips back in, and the other serves as a dummy wrist pin to get all those loose needles back into the small end of the connecting rod.
I run my engine at 6250 RPM static. ( maximum torque ) High RPM on the larger engines will probably shorten your crankshaft life. ( At 5000 RPM a ball bearing should run 1500 hours
in oil mist before there is any detectable wear.) Some won't agree with this, but most folks don't run around in their cars using only first gear unless they are drag racing or hill climbing.
If you have a short field, or an underpowered plane, then you might need to pitch for maximum horsepower, but don't expect fuel economy or a long engine life. Static RPM will vary a
bit due to atmospheric air pressure, humidity, and fuel temperature.
My own engine is run on 87 octane regular unleaded car gas. Aviation fuel will cause a more rapid and difficult to remove carbon build-up. I use AV gas when traveling, but prefer the 87
octane car fuel when I can get it. I use no additives as these can cause carbon or ash on the plugs. I store my mixed fuel in plastic containers.
My Chinook with this Rotax 582 will "motor around" and maintain altitude at 4000 RPM when solo. If I am in a hurry, I might turn 5000 RPM, but I take it easy on the engine, so the
power will be there when I need it.
Please check Rotax fuel consumption chart for 4000 RPM. I get better fuel mileage than my 447 Quicksilver did. Rule of thumb is about 20 miles per gallon.
Biggest mistakes I see people make with these engines:
stuck ring allows blow-by, and this takes the oil off of the cylinder wall. A seizure is then likely. Max deviation near the ports is .0015 inch. Above you can see some visible sreaks from
carbon below the exhaust port. You can still see plenty of the cross-hatch. This engine has original piston, cylinders, and rings.
You cannot check for stuck rings by looking in the exhaust port. They usually get stuck near the anti-rotation pin on the intake side of the piston.
When removing the rings to de carbon the grooves, be sure to keep the same ring on the same piston and the same face up. These parts are matched to the cylinder. They will last
for years if you do this properly.
New rings require honing, and if the engine has many hours, boring and honing to put the cylinder round. This gets more expensive.
If regular de-carboning is not done, rings can get so stuck, that a new piston and a bore job would be required, and this will be costly.
I am often asked what type oil I use: Pennzoil AIR COOLED, and de carbon at no more than 350 hours. ( I favor mineral oil and am not stuck on Pennzoil, but it works very well.)
It costs me very little to keep my engine running, but I do my own work. The Rotax does require some special tools to work on it, but they are not expensive. I make my own tools as
shown above. One tool helps pop those wrist pin circlips back in, and the other serves as a dummy wrist pin to get all those loose needles back into the small end of the connecting rod.
I run my engine at 6250 RPM static. ( maximum torque ) High RPM on the larger engines will probably shorten your crankshaft life. ( At 5000 RPM a ball bearing should run 1500 hours
in oil mist before there is any detectable wear.) Some won't agree with this, but most folks don't run around in their cars using only first gear unless they are drag racing or hill climbing.
If you have a short field, or an underpowered plane, then you might need to pitch for maximum horsepower, but don't expect fuel economy or a long engine life. Static RPM will vary a
bit due to atmospheric air pressure, humidity, and fuel temperature.
My own engine is run on 87 octane regular unleaded car gas. Aviation fuel will cause a more rapid and difficult to remove carbon build-up. I use AV gas when traveling, but prefer the 87
octane car fuel when I can get it. I use no additives as these can cause carbon or ash on the plugs. I store my mixed fuel in plastic containers.
My Chinook with this Rotax 582 will "motor around" and maintain altitude at 4000 RPM when solo. If I am in a hurry, I might turn 5000 RPM, but I take it easy on the engine, so the
power will be there when I need it.
Please check Rotax fuel consumption chart for 4000 RPM. I get better fuel mileage than my 447 Quicksilver did. Rule of thumb is about 20 miles per gallon.
Biggest mistakes I see people make with these engines:
- Over revving the engine. Don't trust that cheap tachometer. Double check you are turning the correct RPM
- Crazy oil. Some of the oils people use may damage rubber seals over time. Be sure your engine gets 50:1. Double check consumption of oil injector pump often.
- Constant tinkering to get the "proper" EGT. Don't use the readings from a delicate and very inexpensive gage as the "last word" on your EGT . Double check your spark plugs
to be sure you are getting the right mixture. It is way better to be rich than too lean. Once set, and mixture is generally correct from the factory, it should not require changing.
EGT readings are only to tell you if something is wrong or different. Some pilots actually cannot fly because they are crippled by that little EGT gage. - Be sure to get your engine rebuilt by someone that knows what they are doing. If you don't do it yourself, better not cut corners. Remember that lots of engine rebuilders talk a
good game, but might know very little about the subject. - There is no "clock" in a piece of steel. It has no idea how many hours it has been in your engine. Wear from operation is your enemy, so try to reduce wear on moving parts.
- When working on these simple engines, be sure to stuff a rag around the connecting rod to prevent unwanted items from entering the crackcase.
- If buying a "used" engine, I would prefer the one with lots of hours and never rebuilt, to one that has been "rebuilt" by someone unknown to me. In any case, a used engine
should be inspected closely. Some parts are "matched" and must be kept together. - Inspect your carburetor sockets by bending them during your pre-flight to keep an eye on age cracking.
- De-carbon the engine regularly. Don't keep going because it still seems to run OK. Be sure to de-carbon the bottoms of the pistons. ( Inverted engines get a bunch of carbon.)
- Before you tighten the cylinders, place the exhaust manifold on without gaskets and lightly tighten. This gets cylinders square with manifold face.
- Be sure your fuel pump pulse line slopes downhill to the engine so oil drains back. Oil in the fuel pump will damp out the pulse.
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| Carbon on piston bottom can be seen here. |
| Tool on the left holds the snap ring. Pushing tool on the right drives in the snap ring with the smack of a plastic hammer. Tool guides off of wrist pin hole. I made these tools for working on my Rotax engines with loose needles in the wrist pin. |